A) Field of the Invention.
This invention relates generally to a method for manufacturing wheel spindles and more particularly, to a method for forming stud holes in the wheel spindle flange and the improved wheel spindle resulting therefrom.
This invention is particularly applicable to and will be described with specific reference to that portion of the wheel spindle manufacturing process in which stud holes are formed in the bearing steel spindle flange and serrated wheel lug nut studs are press-fitted therein with minimal flange distortion. However, those skilled in the art will recognize that the invention has broader application and can be applied to any manufacturing process wherein studs, shafts or splines are to be pressed into holes formed in flat steel surfaces such as flanges, ribs, spokes and the like with minimal distortion in the flat surface.
B) Prior Art.
Known wheel bearings of the type shown in FIG. 1 and indicated generally at 10, have a stationary outer hub 12, which is secured to a non illustrated vehicle suspension, and a rotatable wheel spindle, indicated generally at 14. Spindle 14 rotates about wheel bearing centerline 38 and it carries the vehicle wheel 16, as well as a brake drum 18. (Alternatively, brake drum 18 is replaced by a rotor if the vehicle is equipped with disc brakes.) Brake drum 18 is mounted to spindle 14 through an open, central circular hub 20. Specifically, spindle 14 includes a cylindrical pilot 24 with an outer surface over which the brake drum hub 20 is inserted, with a very close radial clearance. A flat annular wheel flange 26 radiates outwardly from the pilot 24, perpendicular thereto, with a flat outer or outboard surface 28 against which the brake drum hub 20 is abutted, and an axially opposed flat inner or inboard surface 30. The brake drum hub 20 is firmly sandwiched between spindle outboard surface 28 and wheel 16 itself, which in turn is bolted onto conventional wheel studs 32, when the vehicle is operating.
Today""s automotive vehicles have improved ride handling characteristics with sensitive and precise steering and braking mechanisms. It is to be appreciated that brake drum hub 20 abuts, in face to face contact, outboard surface 28 of spindle 14 and that wheel 16 similarly contacts brake drum hub 20 so that spindle flange 26, brake drum hub 20, wheel 16 and tire 22 all rotate as one unit when the vehicle is in motion. So long as wheel flange 26 retains perpendicularity with wheel bearing centerline 32 throughout rotation, all components rotate consistently uniform. However, if the flatness of outboard surface 28 is warped or distorted, a lateral movement of all components will be experienced during each wheel rotation which is commonly referred to as lateral run out or LRO in the art. While LRO may occur for any number of reasons, variations in the flatness of outboard surface 29 contributing to LRO produces undesirable effects on the handling characteristics of the vehicle. For example, if spindle flange 26 is or becomes excessively wrapped, the vehicular operator will sense a pulsation in the brake pedal as the brakes are applied and seat against rotating brake drum hub 20. That is, seating of the brakes will not be uniform because LRO causes the drum to axially slip relative to the brakes and non-uniform seating will produce a force pulsation felt in the brake pedal. This pulsation is not desirable especially in performance or luxury vehicles. Similarly, the long lever arm between tire/road contact and stud circle significantly increases tire displacement attributed to LRO during each wheel rotation. The axial displacement is absorbed by the tire""s side wall but not without an adverse effect on the handling characteristics of the vehicle. It is also possible to detect the LRO affects in the vehicle""s steering wheel. The discerning car buyer will not purchase a vehicle if the steering is not precise, stable and solid at all vehicular operating speeds.
Wheel spindles are generally formed as forgings from bearing steels. The bearing races in the spindle are locally heat treated such as by induction heat treating methods to relatively high hardness. The remainder of the wheel bearing spindle is at a low hardness such as that produced by the conventional normalizing heat treat process to which the spindle is initially subjected to. Localized heat treat is necessary because outboard and inboard flange surfaces 26, 28 are machined flat. In particular, outboard surface 28 is machined flat to within a tolerance expressed in microns. Stud holes as well as other holes are then formed in the flange for wheel studs 32. Wheel studs 32, which have serrations for an interference fit, are then pressed into the stud holes. The interference fit is such that the stud must shear before it can rotate in the stud hole. The force required to press the studs into the stud holes is large. While flange outboard surface 28 is securely supported or backed up during the stud pressing step, one of the underpinnings of the invention is the recognition that the forces required to press the studs into the wheel flange at the required interference press fit can cause or contribute to flange distortion and LRO no matter what jigs or fixtures are used to support and/or clamp the wheel flange during the stud pressing step.
Accordingly, one of the major objects of the invention is to provide a method for forming a hole(s) into a flat surface, particularly a wheel spindle flange, into which studs, splines, shafts and the like can be press-fitted with a minimal flange distortion force.
This object along with other features of the invention is achieved in a method for forming an opening in a bearing metal flange into which is pressed a serrated shaft comprising the steps of providing a blanking die having an opening on one side of the flange (bottom side) and a punch having a diameter smaller than the blanking die opening at the opposite side of the flange (top side) and forcing the punch through the flange to produce a frusto-conical, axially-extending flange opening having a minor diameter equal to the punch diameter at the top flange side and a major diameter equal to the blanking die opening at the bottom flange side. A coining punch of diameter equal to or greater than the shaft major diameter is next provided and the coining punch is forced into each end of the frusto-conical opening a set axial distance sufficient to extrude, at least in the frusto-conical opening adjacent the minor diameter, a work hardened upset mass while providing countersunk openings at the axial ends of the frusto-conical opening. A serration punch is then provided and the punch is forced through the frusto-conical opening from the top flange side to produce a cylindrical stud hole axially extending between the countersunk openings while shearing the work hardened upset metal mass from the frusto-conical opening and forming radially outwardly extending serrations which extend for some axial distance in flange metal that is in a substantially non-work hardened state whereby the studs can be pressed through the substantially non-work hardened axial section of the hole with less force than that required if the hole surfaces were conventionally work hardened.
In accordance with another aspect of the invention, a method is provided for assembling studs in a machined flange of a wheel spindle which includes the steps of forming a plurality of circumferentially spaced stud holes axially extending through the flange with substantially non-work hardened hole surfaces. The process then coins stud holes at the inboard and outboard flange surfaces so that countersunk holes of approximately equal diameter extend approximately set axial distances into each stud hole. A stud is provided for each hole having a flat head, a threaded stem and a serrated shank portion between the head and threaded stem and the studs are pressed into the holes such that each stud""s serrated shank portion extends into its respective stud hole whereby the pressing force exerted on the studs is transmitted to and at least partially absorbed by the substantially non-work hardened flange metal adjacent each hole spaced from the inboard and outboard flange surfaces. In accordance with this aspect of the invention, by providing countersunk openings at inboard and outboard flange surfaces terminating at an axially extending hole having a hole surface substantially in a non-work hardened state, the deformation in the axial hole is only from serrations pressing into the flange metal during the stud pressing operation which occurs principally in the xe2x80x9csoftxe2x80x9d flange center and not at the flange face surfaces so that whether the holes are drilled or punched (as described above), flange face distortion or warpness resulting from the stud press step is substantially reduced.
In accordance with another feature of the invention, preferred geometrical relationships are established when the stud holes are punched through a flange which produces an axial hole surface that is in a substantially non-work hardened state.
In accordance with yet another feature of the invention, certain geometrical relationships are established to produce an axially extending hole positioned between two countersunk openings which minimize flange face distortion when a non rotating 5 spline is pressed into the axial extending hole.
In accordance with a still further aspect of the invention an improved wheel spindle of bearing steel is provided having an unpressed and a final configuration. The spindle has a longitudinally extending shaft about which the spindle rotates and a flange extending radially outward from the shaft and perpendicular to the shaft""s axis of rotation. The flange has a plurality of wheel stud holes axially extending therethrough at circumferentially spaced increments with a surface hardness of a divided hole in the unpressed condition and a wheel stud having a serrated section press-fitted in a non-rotational manner into and extending through each wheel stud hole in the assembled condition. In the preferred embodiment, each stud hole has a countersunk bore at each axial end axially extending into each stud hole a set distance whereby each stud hole axially extends through the flange a distance less than the thickness of the spindle flange whereby LRO is reduced. Depending on flange face and wheel hole geometry, one countersunk bore may be sufficient to shift the bolt distortion zone to avoid flange distortion.
It is thus one of the major objects of the invention to produce a wheel spindle flange with studs press-fitted in holes therein in which the wheel spindle flange has minimal LRO.
It is another general object of the invention to provide a method for forming a hole(s) in a flat, rotating surface such as a flange, spoke or the like (particularly stud holes in the flange of a wheel bearing spindle), through which a non-rotational bolt, stud, spline or the like is press-fitted, that minimizes lateral run out, particularly lateral flange run out, when the surface (particularly the wheel bearing spindle) is rotated about its center. Another general object of the invention is to provide a method for forming a hole(s) in a flat surface of a flange, spoke or the like (particularly stud holes in the flange of a wheel bearing spindle), through which a non-rotational bolt, stud, spline or the like is pressed at a minimal press force to establish a press fit.
It is another object of the invention to provide a method of pressing wheel studs into the stud holes in the bearing flange of a wheel bearing spindle with minimal bolt pressing force and/or minimal flange force distortion whether the holes in the bearing flange are pressed or drilled.
A yet more specific object of the invention is the provision of an improved method for punching wheel stud openings in the flange of a wheel spindle in which one or more or any combination of the following advantages are obtained:
1) reduced tonnage and improved tool life at the bolt hole pierce, hole serration and/or bolt pressing steps;
2) minimization of press fit zone distortion at the face surfaces of the flange by axial centering of the press zone between the hole and mating bolt;
3) minimizing of broken slug segments occurring in the hole serration forming step to avoid potential problems of drum or rotor seating against flange face;
4) improved through production by minimizing spalling in the stud holes when hole serrations are formed;
5) utilization of conventional punches and dies in all forming steps of the process thereby obviating the need for expensive, specially designed tooling;
6) consistently produced serrated holes attributed, at least in part, to forming serrations in metal which has not been significantly work hardened;
7) faster production cycles than achieved with drilled holes by punched holes having similar metallurgical characteristics (hardness) to drilled holes; and,
8) improved torque locking of stud in stud hole.
Still another object of the invention is to provide an improved wheel spindle.
These and other object, features and advantages of the invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment taken together with the accompanying drawings.